Barrel engine configurations, such as the general class of engines shown in U.S. Pat. No. 5,749,337 to Palatov, hold potential for high power density packages. This is desirable in many applications, particularly those requiring mobile power sources such as automotive, marine and aviation. Barrel engines typically involve a grouping of power cylinders and pistons arranged in a circle with their axes parallel to a central power shaft. The geometry of the barrel engine requires that the intake and exhaust valves be actuated in a manner that is different than traditional in-line or vee-type engines. Conventional in-line or vee-type engine configurations commonly utilize a longitudinal camshaft, parallel to the primary crankshaft that includes actuation lobes for each intake and exhaust valve or valve set per cylinder. This conventional cam is driven via gear, chain, or belt drive from the primary crankshaft with valve timing dependent upon proper assembly of the components.
A barrel engine is not well suited to use a traditional longitudinal camshaft since the intake and exhaust valves actuate in a direction that is parallel to the axis of the main power output shaft (crankshaft). Plate-style cams are often used to actuate the valves of a barrel engine. In plate cam designs, the cam is generally flat and extends perpendicularly from the main output shaft. The plate cam has a contoured surface that engages valve stems or lifters to actuate the valves, which are generally perpendicular to the plate. Although this configuration reduces parts count, there are several disadvantages. Among them are the deformation of the cam plate as a result of high force requirements to actuate the exhaust valves as compared to the stiffness of the plate and plate-to-shaft attachment. Also, the plate cam design is difficult to design such that sufficient stiffness exists without undue component weight. This is compounded as the interface to the shaft is considered. Other disadvantages include the complexity of manufacturing a plate cam to actuate the valves as compared to conventional cam grinding techniques. The ability to include hydraulic lifters or to incorporate mechanical lash adjustment is also made more complicated by a plate cam design.